Plastic trash bags and wrappers are primarily made of hydrocarbon polymers such as polyethylene, polypropylene, or polyvinyl polymers. While hydrocarbon polymers can be useful for commercially manufacturing trash bags and wrappers having adequate flexibility and puncture and tear resistance, they are resistant to degradation and mineralization and have a tendency to build up in land fills. Under most conditions, hydrocarbon polymers take a long time to decompose. In addition, hydrocarbon polymers are not manufactured from renewable resources.
Hydrocarbons have been combined with starch in attempts at increasing degradability. Trash bags which incorporate starch can be physically degradable, which means that they become broken into many small parts as the starch biodegrades. The hydrocarbon component, however, remains resistant to degradation and mineralization. In certain circumstances, it is believed that the hydrocarbon component has a tendency to encapsulate the starch thereby preventing further biodegradation of the starch. Furthermore, materials incorporating large amounts of starch can be very sensitive to moisture and can have mechanical properties which vary considerably with humidity.
Attempts have been made at developing thermoplastic films having degradable properties. For example, U.S. Pat. No. 4,133,784 to Otey et al. describes degradable mulch films with improved moisture resistance prepared from starch and ethylene/acrylic acid copolymers. U.S. Pat. No. 5,091,262 to Knott et al. describes a multilayer polyethylene film containing a starch filled inner layer, and prodegradant filled outer layers. U.S. Pat. No. 5,108,807 to Tucker describes a multilayer thermoplastic film having a core layer made of polyvinyl alcohol, and outer layers made of polyethylene and prodegradant. U.S. Pat. No. 5,391,423 to Wnuk et al. describes multilayer films prepared from various biodegradable polymers for use in disposable absorbent products, such as diapers, incontinent pads, sanitary napkins, and pantyliners.
Many biodegradable polymers have been found to possess the desirable characteristics of biodegradability and compostability. At room temperature, however, many biodegradable polymers are either too brittle to provide the desired puncture and tear resistance necessary for commercially acceptable trash bags, or they do not have adequate stability for storage and transport. In addition, many biodegradable polymers are difficult to process into films using commercial manufacturing lines.